1. Field of the Invention
The present invention relates to a synchronous control method in a plurality of channel units and a circuit using said method for synchronously controlling a transmission operation of the plurality of channel units. In a synchronous transmission system, each frame of the transmission signal of a plurality of channels is synchronized thereamong. To execute the frame synchronization, transmission operation in each channel unit by which a transmission signal is transmitted, is controlled synchronizedly. In the synchronous control of the channel units, a necessary synchronous control method is executed corresponding to combinations of the channel units.
2. Description of the Related Art
The synchronous transmission system, for example, receives 150 Mb/s inputs having three 50 Mb/s signals by three channel units in a transmission process circuit, multiplexes the same to 150 Mb/s to transmit by a multiplex circuit, separates the multiplex signal into three 50 Mb/s signals by a separation circuit of a reception process circuit, and the separated signals are output from three channel units.
In this synchronous transmission, since frame positioning of the transmission signals is carried out in the three channel units of the transmission process circuit and three channel units of the reception process circuit, synchronous control circuits are provided in the transmission process circuit and the reception process circuit, and the synchronous control circuit supplies the synchronous control signal to the channel units of the transmission process circuit and the channel units of the reception process circuit for synchronous control.
When the plurality of channel units are transmitted and synchronized, since applied channel numbers and combinations of the channel units are already determined, the necessary synchronous control circuit is used in response to the combination.
While, for effective utilization of lines, particularly at a high speed condition of transmission, there is a request for arbitrary synchronized channel numbers by various combinations of the channel units.
In this constitution, hitherto, since the synchronous control circuit is used corresponding to a combination of the channel units, the synchronous control circuits that are the same number as the channel units combination, must be provided, and moreover, there is a problem in that all the combinations are not always carried out.
Also there is another problem in that when 150 Mb/s circuit is added to another 150 Mb/s circuit to expand the system, the synchronous control cannot be carried out within the system, the expansion of the system is difficult, and the circuitry must be changed in response to the application aspects.